Sonographic Findings in Muscle Strain Injury: Clinical and MR Imaging Correlation

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1 Sonographic Findings in Muscle Strain Injury: Clinical and MR Imaging Correlation Shigeo Takebayashi, MD, Haruo Takasawa, MD, Yuko Banzai, MD, Hideyuki Miki, MD, Ryousuke Sasaki, MD, Yoshinori Itoh, MD, Sho Matsubara, MD Both sonography and magnetic resonance imaging were performed in 57 patients with clinically suspected strain injury in lower extremity muscles. Sonography demonstrated normal findings in nine patients (16 %), hyperechoic infiltration in 31 patients (54%), mass in nine patients (163 ), and compound lesions of infiltration and mass in eight patients (14%). Clinically grade 2 lesions ranged from small infiltration to large compound lesions on both sonography and magnetic resonance imag- M uscle strain, a common sports injury, involves the stretching or tearing of a musculotendinous junction.1 Orthopedists have assessed the severity based on signs, symptoms, and the results of manual muscle testing. Imaging evaluation of muscle strain may be helpful in ascertaining the appropriate times for athletes to begin training or to return to athletic competitions,2 because too early a return to athletic activities may cause further muscle strain injury.3 Recently MR ing. Hyperechoic infiltration was not demonstrated on Tl-weighted magnetic resonance images and with less than 5% cross-sectional muscle involvement. The mass and compound lesions were ascertained to be moderate or severe injury because the masses of the lesions had obvious hemorrhage or hematoma on magnetic resonance images. KEY WORDS: Sonography; Muscle, injury; MR imaging; Sports medicine. imaging has been used in characterizing muscle strain injuries-hi and predicting appropriate convalescence times.2 Sonography using 7.5 MHz transducers permits impressive visualization of the internal architecture of musdes.7.8 In this study, we evaluated the usefulness of the sonography in diagnosis of muscle strain injuries and correlated sonographic findings with clinical grades and MR imaging findings. PATIENTS AND METHODS ABBREVIATIONS MR, Magnetic resonance; SE, Spin t.'cho; STIR, Short Tl inversion n.>covery; FOV, Field of view; TR, Repetition time; TE, Echo time; Tl, Inversion time; SD, Standard deviation R1.>ceiv1.>d May 1, 1995, from the Departments of Radiology (5.T., Y.B.. Y.I.) and Orthopedics (H.T.. H.M, R.5.), Yokohama City Kowan Hospital and the Department of Radiology, Yokohama City University Hospital (S.M.), Yokohamn, Jnpan. Revised mnnuscript acceplt.'l.i for publication July 3, Address correspondence and reprint requests to Shigeo Takebayashi, MD, Department of Radiology, Yokohama City Kowan Hospital, 2-3-2, Shin-Yamnshita, Naka-ku, Yokohamil, 231, Japan. From October 1993 to January 1995, we performed both sonography and MR imaging of lower extremity muscles in 57 patients who had experienced a sudden pain in thighs (46 patients) and calves (11 patients) during athletic activities. The study group consisted of 37 men and 2 women ranging in age from 15 to 36 years (mean, 22 years). Three different blinded reviewers were involved in this study. One reviewer performed the clinical grading, the second reviewer performed sonography, and the third reviewer performed MR imaging. One of the authors made the clinical diagnosis of muscle strain injuries and assessed the severity of the injuries according to 1995 by the American Institute of Ultrasound in Medicine J Ultrasound Med 14:899-95, /95/$3.5

2 9 MUSCLE STRAIN INJURY manual muscle testing as follows: grade 1 (mild degree) is characterized by neither discernible loss of strength nor any restriction of motion; grade 2 (moderate degree) consists of any degree of loss of strength short of complete loss of strength and function; and grade 3 (severe degree) consists of complete loss of strength and function.9 Sonography using a 7.5 MHz transducer (CL 65 system, Aloka, Tokyo, Japan) was perfonned within 1 to 1 days (mean, 2.6 days) after the injuries. One of the authors, blinded to the clinical grades of the injuries, scanned the muscles, compared with contralateral part, and marked the skin superficial to the muscle injuries. Sonographic findings of the muscles wen~ classified into four types as (1) nonnal findings, (2) hyperechoic infiltration, (3) mass, and (4) a compound lesion of hyperechoic infiltration and mass. The masses were subdivided according to echogenic ity in comparison to that of intact muscles. MR imaging was performed within 3 hours after sonography using a.5 T superconducting system (Gyroscan TS II, Philips Medical Systems International, Best, The Netherlands). A wraparound body surface coil (a flexible coil designed to be wrapped around the patient's body, 1 cm x 25 cm) was used for the images of thighs and wraparound extremity surface coil (16 cm x 13.S cm) was used for the iinages of calves. The coils covered the thighs or calves, including the marks on the skin identifying the injury sites. Three different pulse set.1uences (SE Tl-weighted, fast SE T2-weighted, and STIR) were used for obtaining transaxial images. Fast SE T2weighted sequences were used for sagittal images. Twelve sections were acquired with a 6 to 1 mm section thickness and a.6 to 1. mm intersection gap. The FOV was 16 to 35 cm. Pulse SL'qUences for SE Tl weighted images were performed with a TR of 5 to 552 ms and a TE of 2 to 25 ms. Two signal acquisitions were used. The scan matrix and reconstruction matrix were 25 x 256 and 256 x 256, respectively. Acquisition time for this sequence was about 4 to 6 min. For the T2-weighted fast SE sequence, parameters were TR, 25 to 3 ms; TE, 9 to 1 ms, echo number, single; echo-train length, 11; signal averaged, six; scan matrix, 2 to 243 x 256; reconstruction matrix, 256 x 256. Acquisition time for this sequence was 4 to 6 min for transaxial or sagittal imagl>s. STIR images were obtained with following parameters: TR/TE/Tl, 15/5/12 ms; scan matrix, 192 x 256; reconstruction matrix, 256 x 256; scan time, 7to1 min. Each observer reviewed the sonograms or MR images regarding (1) what specific muscles were J Ultrasound Med 14:899-95, 1995 involved, (2) what percentages of the muscle's crosssectional area were involved on sonograms or STIR images (the size of the lesions was classified according to the maximal percentage of the muscle crosssectional area as follows: small, less than 2%; moderate size, 2 to 5 %; large, greater than 5%), (3) perimuscular or peritendinous fluid collection, and (4) tendon tear. The sonologist classified the appearance of echogenic borders of the involved muscles into normal, thickening, and disruption. The reviewer of the MR images documented the presence of intramuscular hemorrhage or hematoma. The convalescence time is defined as the period from the date of muscular injury to the patient's return to active participation. In all patients, the con valescences were predicted according the findings of MR imaging3 as 3 weeks for mild strain, 6 weeks for moderate or severe strain.io At the convalescence times, exercises were allowed in stepwise fashion according to changes in the signs and symptoms. The first step was stretching and walking when pain had disappeared. The second step consisted of jogging when tenderness had subsided and no pain occurred on walking. The third step included a dash at half of maximum speed when tenderness had subsided and the degree of pain was decreased on stretching. The fourth step was 8% muscle training when no pain occurred on stretching.3 In all patients, we correlated the sonographic findings with clinical grade of injury and MR imaging findings as the gold standard. The comparisons were made between patient groups based on (1) mean periods from onset of the injury to sonography, (2) mean convalescence times, and (3) the frequency of each clinical grade. We also compared mean percentage of cross-sectional muscle involvement on sonography with that on STIR imaging. Student's ttest and chi-square analysis were used in statistical comparison. At 2 weeks after initial sonography, follow up sonography was performed in 28 of 57 patients. The improvement of pain and tenderness at the follow-up examination was correlated with the changes in sonographic findings. RESULTS The injured muscles were clinically suspected of being the hamstring group in 21 patients (37%), the quadriceps group in 25 patients (44%), and calf muscles in ll patients (19%). Table 1 demonstrates sonographic findings of muscle strains correlated with clinical grades of the injuries and mean periods from

3 J Ultrasound Med 14:899-95, 1995 TAKEBAYASHI ET AL 91 Table 1: Sonographic Findings of 57 Muscle Strain Injuries Correlated with Mean Period Trauma and Clinical Grade Clinical Grade Normal findings No.(%) of Mean period (SD) Patients from Trauma to US 5.7 (3.1) 9(1) 14 (45) 31 (54) 5.S (4.) 9 (16) 5.4 (3.6) Compound of infiltration and mass 8 (14) 5.1 (1.7) Hyperechoic infiltration Total No. (%)of patients 9 (16) Masses 57 Percentage of Muscle Cross3 <2% 17 (55) 6 (67) 23 (4) sectional Area on Sonography 2 3(33) 6 (75) 2(25) 29 (51) 5 (9) 21 (68) 21 (37) 2-5% 5%< 1(32) 3(33) 6(67) 2(25) 6(75) 15 (26) 12(21) The numbers in parentheses indicate percentage. injury. No statistical difference was found in the mean time from trauma among the patient groups. The lesions included seven mixed echogenic masses and two hypoechoic masses among the nine mass lesions; two hypoechoic masses (Figs. 1, 2) and six mixed echogenic masses were seen in the eight compound lesions. Masses or compound lesions on sonography correlated with higher clinical grades and larger involvement of muscles than infiltrative lesions. None of the infiltrative lesions was clinically assigned to grade 3 injury. Masses or compound lesions had significantly higher rates of grade 3 injury than infiltrative lesions (P <.1). Although the prevalence of grade 1 injury was significantly higher in infiltrative lesion than in masses (P <.1) or compound lesions (P <.5). Clinically grade 2 injuries ranged from small infiltration to large compound lesions. MR imaging with all pulse sequences revealed normal muscles that were also normal on sonograms. No mass was identified on MR imaging when one was not seen on sonography. Thirty-one patients had hyperintense signal infiltrating the muscles on STIR imaging. In each case, the infiltrative appearance on MR imaging resembled that seen on sonography. None of the muscles with hyperechoic infiltration was hyperintense on the Tlweighted sequence. Twenty-two (71 %) of the 31 infiltrated muscles were hyperintense on the T2weighted sequences. The remaining nine small infiltrations were subtle on T2-weighted sequences but highlighted by STIR sequences (Fig. 3). Not all infiltrations of the compound lesions were definitely detected with Tl-weighted image, but they all were with T2-weighted image. Tl-weighted MR images demonstrated high signal intensity in all masses, including those in the compound lesions (Fig. 1C). Eleven masses with mixed echogenicity and four hypoechoic masses exhibited high signal intensities on T2-weighted images (Fig. lb). In the remaining two mixed echogenic masses, T2-weighted images revealed hypointense rims of hemosiderin. The mean percentages of the involved muscle areas were 28.5 ± 23.5% (5) on sonography and 29.4 ± 23.7% on STIR imaging (no statistical difference). Sonographically, the borders of the muscles with infiltration were thickened in 13 patients and par tially disrupted in four patients. The borders of all muscles involved by masses or compound lesions were partially disrupted. Sonography detected tendon tears (quadriceps and gastrocnemius tendons) in only two patients (4% of the five patients with tendon tears on MR imaging). MR imaging detected perimuscular fluid collections in 18 patients, including eight patients (44%) in whom sonography detected perimuscular fluid. No correlation was seen between thickening or disruption of the muscular border and perimuscular fluid collection on MR imaging. The patients with normal sonograms were allowed to return to usual athletic activities in a few days. The mean convalescence times were 2 to 4 days (mean, 3.2 ±.8 days) in normal findings, 12 to 36 days (mean, 2.2 ± 5.2 days) in infiltrative lesions, 32 to 52 days (mean, 45.8 ± 9.6 days) in masses, and 38 to 56 days (mean, 46.5 ± 7.2 days) in compound lesions. The mean convalescence time in infiltrative lesions was significantly shorter than that in masses or compound lesions (P <.5). Follow-up sonography at 2 weeks after initial sonography was performed in 11 patients with hyperechoic infiltration, nine patients with masses, and five patients with the

4 92 MUSCLE STRAIN INJURY J Ultrasound Med 14:899-95, 1995 A Figure 1 An 18 year old sprinter with clinically grade 2 (moderate) muscle strain injury in right hamstring muscle group. The injury occurred 4 days before imaging. A, A transverse sonogram of semitendinous and semimembranous muscles shows a compound lesion consisting of hyperechoic infiltration (slrort arrows) and hypoechoic mass (111g arrows). Arrowhead shows disruption of fascia. F, Femur; A, Adductor magnus muscle. B, A TI-weighted MR image demonstrates marked high signal intensity (111g arrow) surrounded with slightly high signal (slwrt arrows) corresponding to the infiltration in A. A, Adductor magnus muscle. C, A TI-weighted MR image demonstrates a high signal intensity lesion (long arrow) corresponding to a hypoechoic mass in A. No definite abnormality of signal intensity corresponding to hyperechoic infiltration in A is seen. compound lesions. Sonography demonstrated that the infiltrative lesions were reduced when pain and tenderness in the legs subsided. The masses were slightly reduced with decreasing echogenicity of the masses on slight improvement of the signs and symptoms. One of the remaining three patients who had compound lesion attended an athletic competition at the convalescence time. The patient's convalescence time extended more than 6 weeks because the compound lesion progressed on follow-up sonography with increasing pain in the leg. Jn the remaining two patients who had large hematomas in rectus femoris muscle, we considered surgical inter- vention, but the patients refused the surgery. Followup sonography demonstrated a slight reduction of the hematoma in these two patients; their convalescence times extended more than 6 weeks. DISCUSSION Histopathologic studies of muscle strain using an experimental animal model have demonstrated muscle fiber necrosis, tissue edema, infiltration of inflammatory cells, and hemorrhage appearing by 24 hours after any rupture of the muscle fibers.n Mild

5 J Ultrasound Med 14:899-95, 1995 TAKEBAYASHI ET AL A f I I '.. I ' '... i ~~.',. "'.....I '--...,,,, \......,...,_.~.t.;... ',1,- '. '1 " '. ~ /. ~ L l. L B Figure 2 A 26 year old sprinter with clinically grade 2 (moderate) muscle strain injury in quadriceps muscle group. The injury occurred 2 days before imaging. A, A longitudinal sonogram of the right anterior thigh demonstrates a compound lesion consisting of hypoechoic mass (111g arrows) in the rectus femoris muscle and hyperechoic infiltration (short arrows) in the vastus intennedius muscle. The echogenic border between the two muscles may merge with echogenic infiltrative area (arrowheads). No perifascial fluid is detected. r, Rectus femoris muscle; v, vastus intermedius muscle. B, A transaxial STIR MR image demonstrates high intensity region involving both the rectus femoris muscle (111g arrow) and the vastus intermedius muscle (short arrow). Small perifascial extension (arrow/reads) is seen. A Tl-weighted image (111 slrow11) demonstrated high signal intensity corresponding to the hypoechoic mass in A. injury with partial rupture of muscle fibers is characterized primarily by inflammation, edema, and, to a lesser extent, hemorrhage.2 However, moderate or severe strains with complete disruption of the fibers are associated with hematomas. Muscle strain injuries have been clinically assessed according to muscle strength and function.9 Clinically assigned grade 1 strain is thought to represent no appreciable disruption. In the grade 2 strain, actual tissue damage that definitely compromises the strength units is suggested. The grade 3 injury is thought to be complete disruption of muscle-tendon unit.9 In this study, however, clinically assigned grade 2 injuries contain lesions of various degrees on MR imaging and sonography. A study using MR imaging2 has demonstrated that longer convalescences than 5 weeks were encountered in muscle strain injuries with greater than 5% cross-sectional muscle involvement and hemorrhage-like signal intensity, but shorter convalescences were seen with involvement of small cross-sectional areas of muscle. Sonography can also depict the muscle strain regardless of the size or severity of the injury. To detect mild strain using sonography, a comparison with the sonogram of the opposite, uninjured muscle is helpful. Hyperechoic infiltration has been suggested to represent heterogeneous textures composed of mild intraparenchymal hemorrhage or edema or both. This type of injury is judged to be mild because it encompasses less than 5% cross-sectional muscle involvement and reveals no abnormal intensity on Tl-weighted MR images. This study demonstrated that short convalescences were seen in injuries with infiltrative lesions. The mass lesions represent moderate or severe injury because the hypoechoic or mixed echogenic masses in muscle strains are obvious hemorrhage or hematoma, corresponding to the areas of high signal intensity on Tl-weighted MR imaging. Long convalescences are predicted in these types of injuries and have been observed in the injury with distal myotendinous junction tear.2 Sonography may depict tendon tears in muscle strain less well than MR imaging because it may be difficult to depict the normal hyperechoic tendon, which is obscured by the hyperechoic infiltration or mass. Echogenic borders of the injured muscles are disrupted or thickened in some muscle strain injuries. Disruptions of the borders have been suggested to represent tears in fascia. Small injuries of peripheral muscles adjacent to fascia may result in thickening of the echogenic border.

6 94 J Ultrasound Med 14:899 95, 1995 MUSCLE STRAIN INJURY B A Figure 3 A 2 year old sprinter with clinically grade 2 (moderate) strain in right hamstring muscle group. The injury occurred 4 days before imaging. A, A transaxial sonogram of dorsolateral thigh demonstrates hyperechoic infiltration (lo11g arrows) in the periphery of the biceps femoris muscle (lo11g llead). The echogenic border of the muscle involved by the infiltration is partially disrupted (s/1ort arrows). No hyperechoic infiltration is seen in the contralateral uninjured muscle. B, A STIR MR image reveals abnormally high signal intensity (arrow) in periphery of biceps femoris muscle (long fiend). This corresponds to the area of infiltration in A. C, A T2weighted MR image demonstrates subtle high signal intensity (arrow) in the periphery of biceps femoris muscle. T1weighted MR images were normal (not slrow11). c MR imaging is being used with increasing frequency to diagnose the injury.2,4,6 However, an MR imaging examination costs roughly three times as much as sonography. Sonography, which is easily available in most hospitals, can readily depict muscle strain and allow differentiation of moderate or severe injuries from mild lesions. In an era when health care dollars are decreasing, less costly but similarly effective diagnostic methods are necessary to continue providing care. REFERENCES 1. Miller WA: Ru pture of the musculotendinous juncture of the medial head of gastrocnemius muscle. Am J Sports Med 5:191, Pomeranz SJ, Heidt RS: MR imaging Jn the prognostication of hamstring injury. Radiology 189:897, Taylor DC, Dalton JD, Seaber AV, et al: Experimental muscle strain injury: Early functional and structural deficits and the increased risk for reinjury. Am J Sports Med 21:19, 1993

7 J Ultrasound Med 14:899-95, 1995 TAKEBAYASHI ET AL Fleckenstein JL, Weatherall PT, Parkey RW, et al: Sportsrelated muscle injuries: Evaluation with MR imaging. Radiology 172:793, Speeer KP, Lohnes J, Garret WE: Radiographic imaging of muscle strain injury. Am J Sports Med 21:89, Yoshioka H, Anno r, Niitsu M, et al: MRI of muscle strain injuries. J Comput Assist Tomogr 18:454, Kaplan PA, Matamoros A, Anderson JC: Sonography of the musculoskeletal system. AJR 55:237, Vincent LM: Ultrasound of soft tissue abnormalities of the extremities. Radiol North Clin Am 26:131, O'Donoghue DH: Treatment of Injuries to Athletes. Philadelphia, WB Saunders 1984, p Okuwaki T: Treatment of muscle strain injuries in athletes (Japanese). J. Clin Sports Med 11:3, Nikolaou PK, Macdonald BL, Glisson RR, et al: Biomechanical and histological evaluation of muscle fiber after controlled strain injury. Am J Sports Med 15:9, 1986